Interactions In And Stability Of Thin Liquid Films

The stability of colloidal dispersions like foam is governed by the interactions in the thin liquid films between the compartments. For a better understanding of the macroscopic foam, single foam films are investigated. The focus of this study is the effect of oppositely charged polyelectrolyte/surfactant mixtures on foam film stability. For this purpose, mainly mixtures of cationic surfactants and anionic polyelectrolytes around the isoelectric point (IEP) are used. Since both components are oppositely charged, they can form highly surface-active complexes. The results of the TFPB measurements show that the general properties of foam films formed from these mixtures are very similar throughout all systems. A reduction of foam film stability is detected slightly below the nominal IEP of the system and very stable foam films are found in the concentration regime above the IEP. However, the surface characterisation of the air/water interface reveals that this phenomenon is not due to a charge reversal at the interface. Furthermore, the results show that the properties of the foam films depend on the polymer chain length and the hydrophilic/hydrophobic balance of the components.

This book is a treatise on the thermodynamic and dynamic properties of thin liquid films at solid surfaces and, in particular, their rupture instabilities. For the quantitative study of these phenomena, polymer thin films (sometimes referred to as “ultrathin”) have proven to be an invaluable experimental model system. What is it that makes thin film instabilities special and interesting? First, thin polymeric films have an important range of applications. An understanding of their instabilities is therefore of practical relevance for the design of such films. The first chapter of the book intends to give a snapshot of current applications, and an outlook on promising future ones. Second, thin liquid films are an interdisciplinary research topic, which leads to a fairly heterogeneous community working on the topic. It justifies attempting to write a text which gives a coherent presentation of the field which researchers across their specialized communities might be interested in. Finally, thin liquid films are an interesting laboratory for a theorist to confront a well-established theory, hydrodynamics, with its limits. Thin films are therefore a field in which a highly fruitful exchange and collaboration exists between experimentalists and theorists. The book stretches from the more concrete to more abstract levels of study: we roughly progress from applications via theory and experiment to rigorous mathematical theory. For an experimental scientist, the book should serve as a reference and guide to what is the current consensus of the theoretical underpinnings of the field of thin film dynamics. Controversial problems on which such a consensus has not yet been reached are clearly indicated in the text, as well as discussed in a final chapter. From a theoretical point of view, the field of dewetting has mainly been treated in a mathematically ‘light’ yet elegant fashion, often making use of scaling arguments. For the untrained researcher, this approach is not always easy to follow. The present book attempts to bridge between the ‘light’ and the ‘rigorous’, always with the ambition to enhance insight and understanding - and to not let go the elegance of the theory.

This book provides a detailed overview and comprehensive analysis of the main theoretical and experimental advances on free surface thin film and jet flows of soft matter. The book outlines the basic equations and boundary conditions and the derivation of low-dimensional models for the evolution of the free surface. At the experimental front, a variety of recent experimental developments is outlined and the link between theory and experiments is illustrated.

Emulsions: Structure, Stability and Interactions is the perfect handbook for scientists looking to obtain up-to-date knowledge about the fundamentals of emulsion science, and those looking to familiarize themselves with the subject in greater detail. As a ‘stand-alone’ source of information, it is also ideal for solving the practical issues encountered daily in the field of emulsion science. While each chapter presents a concise review on a specific topic, the book offers a consistent presentation of the important physical concepts relevant to emulsions. Some of the topics covered include statistical mechanics of fluid interfaces, the structure of fluid interfaces determined by neutron scattering, hydrodynamic interactions and stability of emulsion films, theory of emulsion flocculation, coalescence kinetics of Brownian emulsions, and Brownian dynamics simulation of emulsion stability. Full and comprehensive presentations Rigorous approach to each topic, providing in-depth information Acts as a 'stand-alone' source of information

This comprehensive reference provided a systematic examination of both the theory and applications of thin liquid films - giving a critical review of major concepts and unresolved or controversial problems, as well as revealing experimental methods. It includes results previously unpublished. Combining the work of 20 leading researchers, Thin Liquid Films furnishes a fundamental overview of thermodynamics of thin liquid films. Generously illustrated with equations, tables and drawling and containing more than 2,200 citations to pertinent literature, this is an authoritative reference for physical, surface, and colloid chemists, biophysicists and physicists; chemical engineers and advanced graduate students in chemistry, chemical engineering, biophysics and physics.

Liquid films having dimensions that are relatively small in the direction normal to their surface are commonly referred to as thin liquid films. Due to their prevalence in nature and due to their unique geometrical characteristics, a comprehensive understanding of thin film dynamics including instabilities and break-up within thin liquid films is of fundamental and practical interest. Practically this understanding is crucial to tuning the stability thin films in a number of important applications such as for stabilizing foams in foods and beverages, destabilizing foams in lubricants, avoiding surface irregularities in liquid coatings and treating ophthalmic disorders originating from the unnatural breakup of the tear film. Fundamentally, the microscopic thickness of these liquid films along with their large surface to volume ratio presents a convenient framework to investigate characteristics of two dimensional flows, and probe the effects of surface phenomenon such as evaporation and surfactant dynamics on fluid flows. Motivated by the importance of thin liquid films, in this thesis, we experimentally investigate the instabilities and break-up within thin liquid films. In the first part of the thesis (Chapters 2 - 4), we develop and optimize experimental tools and protocols for systematically studying thin liquid films. Notably, we show that single bubble/drop experiments are a convenient and complementary technique to study the dynamics of thin liquid films. Subsequently, we detail a new technique for automatically and robustly measuring the spatiotemporal thickness of thin liquid films - hyperspectral interferometry coupled with machine learning. Finally, we will also establish the operating regimes within which the size of bubbles formed on capillaries for single bubble experiments can be precisely controlled to avoid an air compressibility driven shape instabilities. In the subsequent parts of the thesis we utilize the developed tools to study four different problems - Bubble stability in worm like micellar (WLM) polymer solutions (Chapter 5), Lubricant foaming (Chapters 6 - 8), Drying of thin polymer films (Chapter 9) and Dewetting of the tear film (Chapter 10). In Chapter 5, we explore a problem relevant for the cosmetic industry, and characterize the drainage characteristics of thin films between bubbles and flat wormlike micellar solution - air interfaces. The supramolecular structure and elasticity of the wormlike micelles alters the dynamics of film drainage in WLM as compared to those in thin films containing pure surfactants. The unique features of film drainage include film elasticity driven 'dimple recoil' and a single step transition to a Newton black film beyond a critical film thickness. In Chapters 6 - 8, we explore a problem relevant for the lubricant industry, and study the stability of thin liquid films in lubricants with and without antifoams. Utilizing single bubble experiments, we reveal that the stability of thin films between bubbles in lubricant base oils are enhanced by Marangoni flows driven by the differential evaporation of the various components in the oil. Fundamentally, we also show that the spatiotemporal characteristics of these Marangoni flows are regulated by the concentration and volatility of the volatile species in the oil. Interestingly when the concentration of the volatile species approaches 50%, evaporation driven Marangoni flows become chaotic, with disordered spatial structure, chaotic fluctuations, spatially invariant mean film thickness statistics, high sensitivity to initial conditions, rapidly decaying spatial correlation and a power spectrum for thickness fluctuation that obeys a power law scaling that closely resembles the Kolmogorov's -5/3rd scaling. In the presence of filtered lubricants with antifoams, we reveal that the stability of thin films are positively correlated to the number of filtration cycles, and inversely correlated to the nominal filter pore size and the initial antifoam concentration. In Chapter 9 we explore a problem relevant for film coating, and study the drying of aqueous polymer solutions. Depending on the polymer concentration and the polymer diffusivities, we show that a classical Rayleigh-Taylor instability can develop within the drying solution. We also present the scaling laws describing the onset time of the instability as a function of the physical properties and initial polymer concentrations of the solutions. In Chapter 10 we report a platform to characterize the thickness of the tear film in vivo. By qualitatively comparing the dewetting characteristics observed in vivo with in vitro experiments, we will show that the mechanisms of dewetting is influenced by the presence of interfacial rheology. Further we also reveal that the spatial locations that are prone to dewetting are determined by the presence of interfacial rheology and the spatiotemporal drainage characteristics of the tear film. In Chapter 11 we summarize the findings in this thesis and discuss a number of interesting venues for future research.

This comprehensive reference provided a systematic examination of both the theory and applications of thin liquid films - giving a critical review of major concepts and unresolved or controversial problems, as well as revealing experimental methods. It includes results previously unpublished. Combining the work of 20 leading researchers, Thin Liquid Films furnishes a fundamental overview of thermodynamics of thin liquid films. Generously illustrated with equations, tables and drawling and containing more than 2,200 citations to pertinent literature, this is an authoritative reference for physical, surface, and colloid chemists, biophysicists and physicists; chemical engineers and advanced graduate students in chemistry, chemical engineering, biophysics and physics.